Golf club head

ABSTRACT

A golf club head having a hollow internal structure, of which a face portion includes, on its internal surface, an intersection portion located in the central portion of the face portion, a C-shaped outer peripheral portion having an opening on the side of a hosel portion, four main ribs extending from the intersection portion up to an outer edge of the face portion, and an intermediate portion located between the intermediate portion and the outer peripheral portion and the hosel portion. The intermediate portion is divided to four areas by the four main ribs. The thicknesses of a toe side area and a heel side area are greater than the thickness of the outer peripheral portion, and the thicknesses of a crown side area and a sole side area are less than the thickness of the outer peripheral portion.

CROSS-REFERENCE TO RELATED APPLICATION

This Application claims priority from Japanese Patent Application No. 2011-132441 filed Jun. 14, 2011, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a golf club head, more particularly to a golf club head which has an improvement by being providing with a back surface thereof with a thick portion.

In most of recently marketed wood club heads, at least a face portion thereof is formed of metallic material. The face portion needs to be so thick as to maintain strength capable of withstanding an impact when a ball is hit. Although currently the size of the head has tended to be increased, large heads of 460 cm³, which is near the upper official limit stipulated by golf rules, have taken most of the share of marketed driver heads because the driver head must be formed in a volume smaller than 460 cm³+allowance of 10 cm³.

If the head size is so expanded, the weight of the face portion is increased. Thus, generally, while reduction of the weight of the face portion has been currently attempted, the thickness of the face portion has been decreased in order to maintain strength of the face portion and a measure of providing the back side of the face portion with ribs has been adopted. For example, Japanese Patent Application Publication No. 2006-141806 discloses that a golf club head includes six ribs extending from a central portion of the face toward the periphery of its face.

If a rib is provided in the shape of a letter X on the central portion of the back surface of the face portion, resilience property of the face portion drops drastically when a ball is hit on the sole side or the crown side off the face center, as compared to a case where a ball is hit on the face center. To solve this problem, Japanese Patent Application Publication No. 2008-36050 discloses that the thickness of four division faces on the back side of the face, which are defined by dividing with ribs is so determined that the thicknesses of the divided faces on the sole side and the crown side are smaller than those on the toe side and the heel side.

SUMMARY OF THE INVENTION

Conventionally, a number of highly resilient heads having coefficients of restitution considerably increased have been invented. However, it has been officially determined that the high-restitution heads whose coefficient of restitution is 0.830 or more cannot be used in a game from 2008 onward. Accordingly, a golf club whose coefficient of restitution at a center of its face portion is suppressed has been currently developed. However, it has been verified that if the coefficient of restitution at the center of the face portion is suppressed, the resilience property of face surface areas other than the center is lower on the sole side than on the crown side.

In view of the above-described problem, accordingly, an object of the present invention is to provide a golf club head in which with the weight of its face portion reduced and the strength of its face portion maintained, the resilient property of its face center is held within a range complying with the golf rule and even if a ball is hit off the face center, substantially the same resilience property as when the ball is hit at the face center can be

To achieve the above object, the present invention provides a golf club head having a hollow internal structure, the golf club head comprising a face portion, a crown portion, a sole portion, and a hosel portion, wherein the face portion contains, on an internal surface, a central portion Of the face portion, a C-shaped outer peripheral portion having an opening on the side of the hosel portion, at least four main ribs extending from the central portion to an outer edge of the face portion and an intermediate portion located between the central portion and the outer peripheral portion or the hosel portion, wherein the intermediate portion is divided into at least four areas: toe side area, heel side area, crown side area and sole side area with the at least four main ribs, wherein the thicknesses of the toe side area and the heel side area in the intermediate portion are greater than the thickness of the outer peripheral portion and the thicknesses of the crown side area and the sole side area in the intermediate portion are less than the outer peripheral portion.

The thickness of the crown side area of the intermediate portion may be defined to be greater than the thickness of the sole side area of the intermediate portion. The thickness of the heel side area of the intermediate portion may be defined to be greater than the thickness of the toe side area of the intermediate portion.

The face portion may contain, on the internal surface, reinforcement ribs extending from the central portion toward the outside of the face portion.

According to the present invention, the C-shaped outer peripheral portion having the opening on the side of the hosel is provided on the internal surface of the face portion. Then, the intermediate portion located on the central side relative to the outer peripheral portion is divided into four areas with at least four main ribs extending from the central portion to the outer edge of the face portion. The thicknesses of the toe side area and the heel side area in the intermediate portion are defined to be greater than the thickness of the outer peripheral portion. The thicknesses of the crown side area and the sole side area in the intermediate portion are defined to be less than the thickness of the outer peripheral portion. Consequently, with a current trend of reducing the weight of the face portion maintained, the strength of the face portion can be secured and the resilience property of the face can be held within a range complying with the golf rules. Furthermore, even if a ball is hit off the face center, a substantially uniform resilience property can be exerted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an embodiment of a golf club head according to the present invention.

FIG. 2 is a back surface view of the face member of the golf club head shown in FIG. 1.

FIG. 3 is a schematic cross-sectional view of the face member shown in FIG. 2, taken along the line III-III.

FIG. 4 is a schematic cross-sectional view of the face member shown in FIG. 2, taken along the line IV-IV.

FIG. 5 is a schematic cross-sectional view of the face member shown in FIG. 2, taken along the line V-V.

FIG. 6 is a schematic cross-sectional view of the face member shown in FIG. 2, taken along the line VI-VI.

FIG. 7 is a schematic cross-sectional view of the face member shown in FIG. 2, taken along the line VII-VII.

FIG. 8 is a front view showing the angles of ribs on the face member shown in FIG. 1.

FIG. 9 is a front view of another embodiment of a golf club head according to the present invention.

FIG. 10 is a front view showing a comparative example of a golf head club.

FIG. 11 is a front view showing the positions of hitting points in simulation of examples.

FIG. 12 is a graph showing a result of the simulation of the embodiment of the present invention.

FIG. 13 is a graph showing a result of the simulation of the comparative example.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment of a golf club head according to the present invention will be described in detail with reference to the accompanying drawings. The sectional views of FIGS. 3 to 7 are intended to make the configuration of this embodiment understood easily, but they are not drawn to scale.

As show in FIG. 1, a golf club head 1 is constituted mainly of a face member 10 having a face portion 11 and a main body member 20. The main body member 20 includes a sole portion 21, a crown portion 22 and a hosel portion 25, those portions being formed integrally. The face member 10 and the main body member 20 are joined together by welding, so that a hollow structure is formed inside the head. The front end side of the golf club head 1 is called toe 23 and the opposite side is called heel 24.

FIG. 1 shows a face on the hollow structure side of the face member 10, i.e., a structure appearing on the rear side thereof expressed with dotted lines. A partially thick portion, a partially thin portion of the face member 10, e.g., ribs 12, 13 are formed on the rear side of the face member 10 as well as an intersection portion 17 and an outer peripheral portion 14. The rear side of the face member will be described below.

As shown in FIG. 2, the rear side face of the face member 10 is constituted of the intersection portion 17 located in the center of the face portion 11, the C-shaped outer peripheral portion 14 having an opening on the hosel portion side and an intermediate portion 15 located between the intersection portion 17 and the outer peripheral portion 14 or the hosel portion 25. The thicknesses of the intersection portion 17, the outer peripheral portion 14 and the intermediate portion 15 in the face member 10 are different from each other, which will be described below.

Main ribs 12 are formed on the surface on the rear side of the face member 10 such that they extend from the intersection portion 17 to an outer edge of the face portion 11. A first main rib 12 a extends from the intersection portion 17 toward the toe side of the crown portion, a second main rib 12 b extends from the intersection portion 17 toward the heel side of the sole portion 21, a third main rib 12 c extends from the intersection portion 17 toward the heel side of the crown portion 22, particularly toward the hosel portion, and a fourth main rib 12 d extends from the intersection portion 17 toward the toe side of the sole portion 21. These main ribs 12 are connected to each other via the intersection portion 17 disposed in the center of the face portion 11. The four main ribs 12 extend from the intersection portion 17 located in the center of the face portion 11 to suppress the resilience property at the central portion of the face portion 11.

The intermediate portion 15 is divided into four areas by the first to fourth main ribs 12 a to 12 d. That is, the four areas are a toe side area 15 a located between the first main rib 12 a and the fourth main rib 12 d, a sole side area 15 b located between the second main rib 12 b and the fourth main rib 12 d, a crown side area 15 c located between the first main rib 12 a and the third main rib 12 c and a heel side area 15 d located between the second main rib 12 b and the third main rib 12 c. On the other hand, although the outer peripheral portion 14 is separated by the main rib 12, the separated areas of the outer peripheral portion 14 have an equal thickness, so that they can be handled as an integral part.

As shown in FIG. 3, the four main ribs 12 are formed so that the thickness of the center of the main rib 12 is the largest while the thickness thereof is reduced toward the neighboring flat outer peripheral portion 14 and intermediate portion 15, that is, the toe side area 15 a and the sole side area 15 b in this case. The main ribs having such a configuration can prevent an impact stress from being concentrated to a point. The reduction of the thickness is preferred to be implemented for the surface of the rib to have a circular curved face. Preferably, the radius of this circle is, for example, 10 mm or more. On the other hand, as shown in FIG. 4, the main rib 12 is formed so that the thickness thereof is equal from the intersection portion 17 toward outside of the face portion 11.

Of the four main ribs 12, at least one main rib may be formed so that the thickness of its thickest portion is different from the thickness of the other main ribs. As shown in FIG. 4, the thickness of the first main rib 12 a is preferred to be greater than the thickness of the second main rib 12 b. Alternatively, the thickness of the third main rib 12 c is preferred to be greater than the thickness of the fourth main rib 12 d. By defining the thickness of the main rib located on the crown side with respect to the center of the face portion 11 to be greater than the thickness of the main rib located on the sole side, the resilience property of the entire face portion 11 can be brought close to equal. The thickness of the first main rib 12 a and the thickness of the third main rib 12 c, both located on the crown side may be equal or different. The thickness of the second main rib 12 b and the thickness of the fourth main rib 12 d, both located on the sole side may be equal or different.

Preferably, a difference in thickness of the main rib between the crown side and the sole at the thickest portion of each rib is approximately 0.2 mm or more, more preferably approximately 0.3 mm or more. On the other hand, the upper limit of the difference in thickness is preferred to be approximately 0.7 mm or less, more preferably approximately 0.6 mm or less. Furthermore, of the first to fourth main ribs 12 to 15, a difference in thickness between a thickest portion of the thinnest main rib and a neighboring peripheral portion 19 is required to be at least approximately 0.3 mm or more, is preferred to be approximately 0.5 mm or more, and is more preferred to be approximately 0.6 mm or more. On the other hand, the upper limit of this difference in thickness is preferred to be approximately 2.0 mm or less and is more preferred to be approximately 1.8 mm or less.

Preferably, the four main ribs 12 are formed in a substantially equal width. The width of the main rib 12 is preferred to be approximately 2 mm or more at a portion in contact with the face back surface, and is more preferred to be approximately 3 mm or more. On the other hand, the upper limit of the width of the main rib 12 is preferred to be approximately 12 mm or less and is more preferred to be approximately 10 mm or less.

Reinforcement ribs may be formed on the back surface of the face portion 11. As the reinforcement rib, as shown in FIG. 2, a toe side reinforcement rib 13 a is formed so that it extends to the toe side area 15 a in the intermediate portion from the intersection portion 17 and a heel side reinforcement rib 13 b is formed so that it extends to the heel side area 15 d from the intersection portion 17. The toe side reinforcement rib 13 a and the heel side reinforcement rib 13 b are arranged linearly across the intersection portion 17. If the resilience property of the intermediate portion 15 such as the toe side area 15 a and the heel side area 15 d is higher than that stipulated by the golf rules, formation of the reinforcement ribs 13 can lower the resilience property of these areas.

The reinforcement rib 13 is formed like the main ribs so that the thickness thereof in the center is the greatest while the thickness decreases toward the intermediate portion. On the other hand, as shown in FIG. 5, the reinforcement rib 13 is so formed that the thickness thereof decreases gradually from the intersection portion 17 toward the outside of the face portion 11. The width of the reinforcement rib 13 is defined to be decreased gradually from the intersection portion 17 toward the outside of the face portion 11. By forming the reinforcement rib 13 gradually thinner and narrower from the center thereof toward the outside, a rapid change in stiffness can be prevented. The tip of the reinforcement rib 13 may be formed circularly. The radius of this circle is preferred to be, for example, 10 mm or more, and is more preferred to be 15 mm or more.

The reinforcement rib 13 may be formed from the center of the face portion up to a halfway position relative to the outer edge. The length of the reinforcement rib 13 is preferred to be approximately 45% or more a distance from the center of the face portion 11 up to the outer edge, and is more preferred to be approximately 50% or more. On the other hand, the upper limit of the length of the reinforcement rib 13 is preferred to be approximately 90% or less and is more preferred to be approximately 85% or less. Thus, the reinforcement rib 13 may be formed in only the intermediate portion 15 as shown in FIG. 2. The lengths of the reinforcement ribs 13 on the toe side and the heel side may be equal or different.

The thickest portion of the reinforcement rib 13 may be formed in the same thickness as a thickest portion of the thickest main rib of the four main ribs 12 or in a lesser thickness or in a greater thickness. Both in the case of increasing and decreasing the thickness, a difference in thickness therebetween is preferred to be approximately 0.1 mm to approximately 0.5 mm. The width of the reinforcement rib 13 is preferred to be approximately 2 mm or more at the thickest portion and is more preferred to be approximately 3 mm or more. On the other hand, the upper limit of the width of the reinforcement rib 13 is preferred to be approximately 12 mm or less and is more preferred to be approximately 10 mm or less.

The outer peripheral portion 14 of the face portion 11 and the four divided intermediate portions 15, i.e., the toe side area 15 a, the sole side area 15 b, the crown side area 15 c and the heel side area 15 d have a substantially equal thickness in each portion. However, as shown in FIG. 6, the sole side area 15 b and the crown side area 15 c in the intermediate portion 15 are formed in a smaller thickness than the outer peripheral portion 14. As shown in FIG. 7, the toe side area 15 a and the heel side area 15 d in the intermediate portion are formed in a larger thickness than the outer peripheral portion 14. By adopting the configuration having the aforementioned thicknesses, the coefficient of restitution of the central portion is decreased and consequently, the coefficients of restitution of the entire face portion 11 can be equalized.

The width of the C-shaped outer peripheral portion 14 is preferred to be approximately 20% or more a distance from the intersection portion 17 of each main rib 12 up to the outer edge of the face portion 11 and is more preferred to be approximately 25% or more. On the other hand, the upper limit of this width is preferred to be approximately 40% or less and is more preferred to be approximately 35% or less.

The difference in thickness between the toe side area 15 a or the heel side area 15 d in the intermediate portion and the outer peripheral portion 14 is preferred to be approximately 0.025 mm or more, more preferred to be approximately 0.05 mm or more and further preferred to be approximately 0.1 mm or more. On the other hand, if the difference in thickness is excessive, no uniform resilience property may be obtained in some cases. Therefore, the upper limit of the difference in thickness is preferred to be approximately 0.5 mm or less and is more preferred to be approximately 0.4 mm or less. Furthermore, the difference in thickness between the sole side area 15 b or the crown side area 15 c and the outer peripheral portion 14 is preferred to be approximately 0.025 mm or more, is more preferred to be approximately 0.05 mm or more and is further preferred to be approximately 0.1 mm or more. On the other hand, if the difference in thickness is excessive, no uniform resilience property may be obtained in some cases. Therefore, the upper limit of the difference in thickness is preferred to be approximately 0.5 mm or less and is more preferred to be approximately 0.4 mm or less.

The thicknesses of the sole side area 15 b and the crown side area 15 c may be equal to or different from each other. However, preferably, to equalize the coefficient of restitution of the sole side with that of the crown side as much as possible, preferably, the thickness of the sole side area 15 b is less than that of the crown side area 15 c as shown in FIG. 6. The difference in thickness is preferred to be approximately 0.025 mm or more, is more preferred to be approximately 0.05 mm or more and is further preferred to be approximately 0.1 mm or more. On the other hand, if the difference in thickness is excessive, no uniform resilience property may be obtained in some cases. Therefore, the upper limit of the difference in thickness is preferred to be approximately 0.5 mm or less and is more preferred to be approximately 0.4 mm or less.

The thicknesses of the toe side area 15 a and the heel side area 15 d may be equal to or different from each other. However, preferably, to equalize the coefficient of restitution of the toe side with that of the heel side as much as possible, the thickness of the toe side area 15 a is less than that of the heel side area 15 d as shown in FIG. 7. The difference in thickness is preferred to be approximately 0.025 mm or more, is more preferred to be approximately 0.05 mm or more and is further preferred to be approximately 0.1 mm or more. On the other hand, if the difference in thickness is excessive, no uniform resilience property may be obtained in some cases. Therefore, the upper limit of the difference in thickness is preferred to be approximately 0.5 mm or less and is more preferred to be approximately 0.4 mm or less.

As shown in FIGS. 4 to 7, the intersection portion 17 has a central portion 18 having the greatest thickness. The intersection portion 17 is formed so that the thickness thereof is decreased gradually from the central portion 18 toward the intermediate portion 15 or the main ribs 12. The central portion 18 contains a sweet spot of the face portion 11, i.e., a gravity center of the golf club head projected onto the face surface. This central portion 18 contains an intersection between the central axis of the first and second main ribs 12 a, 12 b and the central axis of the third and fourth main ribs 12 c, 12 d. The intersection of the main ribs and the sweet spot may be on the same point or on different points. Furthermore, the intersection of the main ribs is disposed so as not to exist on a score line formed on the surface of the face portion 11 or on an extension of a score line (not shown) formed partially on the toe side and the heel side of the face portion.

The thickness of the central portion 18 is greater than the thickness of a thickest portion of the main rib having the largest thickness of the four main ribs 12. A difference in thickness is preferred to be approximately 0.1 mm to approximately 0.5 mm. Furthermore, as shown in FIG. 2, the central portion 18 is preferred to be flat and circular. The radius of the flat and circular central portion 18 is preferred to be approximately 5 mm or more to approximately 12 mm or less. In the meantime, the central portion 18 is not restricted to such a circular shape, but may be of an ellipse or a quadrangle such as a rectangle, a diamond or a polygon such as a pentagon or a hexagon.

As shown in FIG. 2, the intersection portion 17 is preferred to be flat and elliptical. The length of the long axis of the flat and elliptical intersection portion 17 is preferred to be longer than the area of the central portion 18 by approximately 20 mm or more and is more preferred to be longer by approximately 30 mm or more. On the other hand, the upper limit of the long axis is preferred to be approximately 50 mm or less and is more preferred to be approximately 45 mm or less. The length of the short axis of the flat and elliptical intersection portion 17 is preferred to be longer than the area of the central portion 18 by approximately 10 mm or more and is more preferred to be longer by approximately 20 mm or more. On the other hand, the upper limit of the short axis is preferred to be approximately 40 mm or less and is more preferred to be approximately 30 mm or less.

Although the thickness of the intermediate portion 15 in the face member 10 differs between the toe side area 15 a, the sole side area 15 b, the crown side area 15 c and the heel side area 15 d as described above, it is preferred to be approximately 1.0 mm or more and is more preferred to be approximately 1.5 mm or more. On the other hand, the upper limit of the thickness of the intermediate portion 15 is preferred to be approximately 3.0 mm or less and is more preferred to be approximately 2.5 mm or less. There exists a difference in thickness between the outer peripheral portion 14 of the face member 10 and the intermediate portion 15 as described above, and the thickness of the outer peripheral portion 14 is preferred to be approximately 1.0 mm or more and is more preferred to be approximately 1.5 mm. On the other hand, the upper limit of the thickness of the outer peripheral portion 14 is preferred to be approximately 3.0 mm or less and is more preferred to be approximately 2.5 mm or less.

Although there exists a difference in thickness between one main rib and another main rib, and between the main rib and the intermediate portion 15 or the outer peripheral portion 14, the thickness of the thickest portion of each of the four main ribs 12 a to 12 d of the face member 10 is preferred to be approximately 3.0 mm or more and is more preferred to be approximately 3.2 mm or more. On the other hand, the upper limit of the thickness of the four main ribs 12 a to 12 d is preferred to be approximately 4.2 mm or less and is more preferred to be approximately 4.0 mm or less. Furthermore, the thickness of the thickest portion of the reinforcement rib 13 of the face member 10 is preferred to be approximately 3.0 mm or more and is more preferred to be approximately 3.2 mm or more. On the other hand, the upper limit of the thickness of the reinforcement rib 13 is preferred to be approximately 4.2 mm or less and is more preferred to be approximately 4.0 mm or less. There exists a difference in thickness between the central portion 18 of the face member 10 and the main rib 12 as described above, and the thickness of the central portion 18 is preferred to be approximately 2.5 mm or more and is more preferred to be approximately 2.7 mm or more. On the other hand, the upper limit of the thickness of the central portion 18 is preferred to be approximately 4.0 mm or less and is more preferred to be approximately 3.8 mm or less.

The first main rib 12 a is preferred to be inclined toward the toe side relative to vertical. Furthermore, the second main rib 12 b is preferred to be inclined toward the heel side relative to the vertical. By inclining the first and second main ribs 12 a, 12 b in this way, the resilience property along a direction from the toe upper side to the heel lower side, where hitting points by amateur golfers concentrate, can be extracted to a maximum extent. More specifically, an angle θa of the central axis 31 of each of the first main rib 12 a and the second main rib 12 b with respect to a ground line 30 when the golf club head 1 is placed on an ordinary address position as shown in FIG. 8 is preferred to be approximately 90° or less and is more preferred to be about 85° or less. On the other hand, the lower limit of the rib inclination angle θa is preferred to be approximately 25° or more and is more preferred to be approximately 30° or more.

The third main rib 12 c is preferred to be inclined toward the crown side or the hosel side relative to horizontal. The fourth main rib 12 d is preferred to be inclined toward the sole side relative to horizontal. By inclining the third main rib 12 c and the fourth main rib 12 d in this way, the resilience property in the upper area of the toe can be extracted to a maximum extent. More specifically, an inclination θb of a central axis 32 of the third main rib 12 c and the fourth main rib 12 d with respect to the ground line 30 is preferred to be approximately 5° or more and is more preferred to be approximately 10° or more. On the other hand, the upper limit of the rib inclination angle θb is preferred to be approximately 80° or less and is more preferred to be approximately 70° or less.

Preferably, a central axis 33 of the reinforcement rib 13 divides an angle formed by the central axis 31 of the first and second main ribs and the central axis 32 of the third and fourth main ribs to equal two parts (that is, the central axis 33 has an angle θc on each side with respect to both the central axes 31, 32). Preferably, an inclination of the long axis of the ellipse of the intersection portion 17 divides the angle formed by the central axis 31 of the first and second main ribs and the central axis 32 of the third and fourth main ribs to equal two parts like the central axis 33 of the reinforcement rib 13.

It is permissible to curve the first main rib 12 a and the second main rib 12 b smoothly in an S shape or a Z shape along the central axis 31 instead of a straight line. Furthermore, it is also permissible to curve the third main rib 12 c and the fourth main rib 12 d smoothly in an S shape or a Z shape along the central axis 32 instead of a straight line. By curving the main ribs 12 smoothly in this way, both the areas of the sole side area 15 b and the crown side area 15 c in the intermediate portion can be increased.

The face member 10 may be formed by forging or casting. As the material of the face member 10, titanium, titanium alloy or stainless steel may be used. The volume of the golf club head 1 is preferred to be approximately 100 cc or more and is more preferred to be approximately 150 cc or more. On the other hand, the volume of the golf club head 1 is preferred to be approximately 500 cc or less and is more preferred to be approximately 460 cc or less. Furthermore, the weight of the golf club head 1 is preferred to be approximately 170 g or more and is more preferred to be approximately 175 g or more. On the other hand, the weight of the golf club head 1 is preferred to be approximately 250 g or less and is more preferred to be approximately 245 g or less.

Although the above-described embodiment contains the reinforcement rib 13 as shown in FIGS. 1 to 7, the present invention allows not providing the reinforcement rib as shown in FIG. 9.

EXAMPLES

A golf club head according to the present invention was manufactured and the coefficient of restitution (COR) of its face portion was evaluated. In this embodiment, a characteristic time (CT) was measured instead of measuring the COR value actually. The CT value is a quantitative value capable of measuring the spring effect of the face adopted by the United States Golf Association (USGA) and the Royal and Ancient Golf Club of St. Andrews (R&A) and can be measured with a portable pendulum machine approved by the R&A Rules Limited. Generally, the more the face is deflected, the less energy is lost and the initial velocity of a ball is higher. Thus, the CT value indicates the deflection with a contact time between the ball and the face. Currently, the upper limit of the CT value is defined to be 257 (defined value of 239+allowance of 18) μseconds.

As the golf club head of this example, the configuration shown in FIG. 2 was adopted. That is, by providing four main ribs and two reinforcement ribs, the face portion was divided into four areas with the four main ribs and the outer peripheral portion so that the four divided intermediate portions have a different thickness each. On the other hand, a golf club head of a comparative example was provided with no outer peripheral portion as shown in FIG. 10 and instead, by extending the intermediate portion up to an outer edge, peripheral portions were formed around the intersection portion. For this example and the comparative example, Table 1 shows the thicknesses of the central portion and the outer peripheral portion, those of the four divided intermediate portions and peripheral portions which are defined by dividing with the main ribs, and those of the four main ribs and those of the reinforcement ribs.

TABLE 1 Comparative Example example Thickness of central portion [mm] 3.75 3.75 Thickness of outer peripheral portion [mm] 2.3 — Thickness of intermediate Toe side area 2.45 2.45 portion (peripheral portion) Sole side area 2.0 2.0 [mm] Crown side area 2.1 2.1 Heel side area 2.5 2.5 Thickness of main rib [mm] First main rib 3.5 3.5 Second main rib 2.8 2.8 Third main rib 3.5 3.5 Fourth main rib 3.2 3.2 Thickness of reinforcement Reinforcement rib 3.5 3.5 rib [mm] on toe side Reinforcement rib 3.5 3.5 on heel side

As the common conditions of the face portion, the width of the face portion was set to 75 mm and the height thereof was set to 43 mm. The first to fourth main ribs were tilted in the same way as FIG. 2. The length of the long axis of the elliptical intersection portion was set to 40 mm, the length of the short axis was set to 30 mm and the angle θc of the ellipse was set to 15°. The width of the C-shaped outer peripheral portion was set within 30 to 40 mm. The length of the reinforcement rib was set to 27 mm for the toe side and 25 mm for the heel side. The width of the first to fourth main ribs was set to 9.5 mm and the width of the reinforcement rib was set to 7.1 mm. As the common conditions of the golf club head, the material of the face member was titanium alloy (Ti-6A1-4V), the volume of the head was 460 cc and the weight of the head was 190 g.

With this example and the comparative example, the CT values were measured at hitting points of a ball. As shown in FIGS. 11 and 15, hitting points of the balls in the vertical direction and the horizontal direction were investigated. A hitting point 40 c at the center assumes hitting of the ball at the sweet spot, and is assumed to be located within the intersection portion of the face member. Other 14 hitting points assume hitting of the ball off the sweet spot. Positions 10 mm away from the central hitting point 40 c toward the toe side and the heel side are assumed to be hitting points 40 b, 40 d, respectively, and positions 10 mm further away toward the toe side and the heel side are assumed to be hitting points 40 a, 40 e, respectively. Positions 10 mm away from these five hitting points 40 a to 40 e toward the crown side and the sole side are assumed to be 40aH to 40eH and 40aL to 40eL respectively.

Under the above-described condition, the CT values of the respective hitting points of the example and the comparative example were measured. Table 2 and Table 3 show the measurement results. Based on those measurement results of the hitting points, the CT values of the entire face portion within the hitting area were calculated. FIG. 12 and FIG. 13 show the measurement results. In these tables and figures, the position of the central hitting point 40 c was assumed to be 0 mm, and a distance toward the crown side or the heel side was expressed with a positive value while a distance toward the sole side or the toe side was expressed with a negative value. The results of the tables and figures were expressed with a ratio when the CT value of the central hitting point 50 c was assumed to be 100. The area surrounded with a bold line in the figures indicates an area whose ratio of the CT value was 96 or more, and each time when a thin line is passed, the ratio of the CT value is increased or decreased by one.

TABLE 2 CT value (ratio) Example −20 mm −10 mm 0 mm 10 mm 20 mm 10 mm 95 97 97 97 99  0 mm 98 99 100 100 95 −10 mm   86 97 99 94 95

TABLE 3 Comparative CT value (ratio) example −20 mm −10 mm 0 mm 10 mm 20 mm 10 mm 94 97 99 97 99  0 mm 96 99 100 99 93 −10 mm   85 97 100 93 94

As shown in Table 2, Table 3, FIG. 12 and FIG. 13, the golf club head of this example having the outer peripheral portion which has a larger thickness than the sole side area and the crown side area in the intermediate portion and having a smaller thickness than the toe side area and the heel side area could equalize the CT of the face portion compared to the golf head club according to the comparative example having no outer peripheral portion. Particularly, uniform CT values could be obtained in an area 0 mm to 10 mm in the height direction and −10 mm to −20 mm off the center and in an area −10 mm to 0 mm in the height direction and 10 mm to 20 mm off the center. Consequently, it can be verified that even when the ball is hit off the sweet spot, a substantially similar resilience property to when the ball is hit off the sweet spot can be achieved. 

1. A golf club head having a hollow internal structure, comprising a face portion, a crown portion, a sole portion, and a hosel portion, wherein the face portion comprises, on an internal surface, a central portion of the face portion, a C-shaped outer peripheral portion having an opening on the side of the hosel portion, at least four main ribs extending from the central portion to an outer edge of the face portion and an intermediate portion located between the central portion and the outer peripheral portion or the hosel portion, wherein the intermediate portion is divided into at least four areas: toe side area, heel side area, crown side area and sole side area with the at least four main ribs, wherein the thicknesses of the toe side area and the heel side area in the intermediate portion are greater than the thickness of the outer peripheral portion and the thicknesses of the crown side area and the sole side area in the intermediate portion are less than the outer peripheral portion.
 2. The golf club head according to claim 1, wherein the thickness of the crown side area of the intermediate portion is defined to be greater than the thickness of the sole side area of the intermediate portion.
 3. The golf club head according to claim 1, wherein the thickness of the heel side area of the intermediate portion is defined to be greater than the thickness of the toe side area of the intermediate portion.
 4. The golf club head according to claim 1, wherein the face portion comprises, on the internal surface, a reinforcement rib extending from the central portion toward the outside of the face portion. 